Generally, automatically shiftable vehicle transmissions in planetary design are already well described in the state of the art, and are subject to continuous development and improvement. Such transmissions preferably features a sufficient number of forward gears, one reverse gear, and a transmission ratio that is well-suited for motor vehicles with a high overall spread, favorable progressive steps, and a sufficiently large start-up transmission ratio for the specific application. In addition, this transmission preferably requires low construction costs, in particular a low number of shift elements and, upon a sequential shifting operation, should avoid so-called “group gearshifts,” such that, when there are gearshifts to the next higher or next lower gear, only one previously engaged shift element is open, and one previously open shift element is engaged.
Such a four-speed automatic transmission emerges, for example, from DE 10 2005 002 337 A1 of the applicant. It essentially comprises one drive shaft, one output shaft, a total of four individual planetary gear sets and five shift elements. By selectively blocking three of the five shift elements designed as clutches and brakes, a total of eight forward gears can be shifted without any group gearshifts.
From DE 10 2007 055 808 A1 of the applicant, a further development of the 8-gear automatic transmission known from DE 10 2005 002 337 A1 is known. Through the kinematic connection of an additional sixth shift element to the existing gear set diagram—specifically in the power flow between two existing shafts of the transmission—two additional forward gears could be represented. Through this sixth shift element formed as a clutch, a clutch shaft, which constantly connects a first planetary gear set that is connectable to the housing to a third planetary gear set that is connected to the output shaft, is now connectable to the second planetary gear set that can be blocked by engaging the fifth of the previously existing five shift elements. Moreover, this additional sixth shift element, in conjunction with the previously existing fourth of the five shift elements, enables the blocking of the third planetary gear set connected to the output shaft. With their transmission ratios, the new gears are between the previous fifth and sixth gears and between the previous sixth and seventh gears of the 8-gear transmission.
From DE 10 2009 001 253 B3 of the applicant, an additional development of the 8-gear automatic transmission is known from DE 10 2005 002 337 A1. Here, by adding a sixth shift element formed as a clutch in the power flow between the drive shaft and the second planetary gear set that can be blocked by engaging the fifth of the previously existing five shift elements, an additional forward gear can be represented, the transmission ratio of which is greater than the previous first gear of the 8-gear transmission. Thus an additional starting gear is created below the previous first gear of the 8-gear transmission.
An additional 10-gear automatic transmission with four individual planetary gear sets and six shift elements is known from U.S. Pat. No. 8,007,394 B2; this differs from the gear set diagram of DE 10 2007 055 808 A1 only in three design details. First, with U.S. Pat. No. 8,007,394 B2, the output shaft is connected only to the planetary gear carrier of the third planetary gear set; the clutch provided with DE 10 2007 055 808 A1 is thus not present in the power flow between the planetary gear carrier of the third planetary gear set and the planetary gear carrier of the second planetary gear. Second, with U.S. Pat. No. 8,007,394 B2, a shiftable connection is provided between the ring gear of the fourth planetary gear set and the sun gear of the second planetary gear set, in place of the constant coupling of the ring gear of the fourth planetary gear set with the sun gear of the second planetary gear set with DE 10 2007 055 808 A1. Third, with U.S. Pat. No. 8,007,394 B2, a clutch is provided in the power flow between the ring gear of the fourth planetary gear set and the planetary gear carrier of the second planetary gear set. Such kinematics of the transmission of U.S. Pat. No. 8,007,394 B2 requires that, for the shifting without group gearshifts of the ten forward gears in each gear, four of the six shift elements are engaged.